1. Field of the Invention
The present invention relates to a variable valve mechanism for an internal combustion engine. More specifically, the present invention relates to a variable valve mechanism that allows a fuel injector to be installed at a location that provides for improved combustion performance, without increasing the width of the engine's cylinder head.
2. Description of Background Information
A variable valve mechanism has been applied to engines used in automotive vehicles as manner of variably controlling the extent and duration of valve lift for a valve that opens and closes an intake port leading to a combustion chamber. Furthermore, a fuel injector is provided to lower undesirable exhaust gas emissions.
The prior art includes a variable valve mechanism, of the type applied to an engine, that includes a camshaft that synchronously rotates with a crankshaft, a solid cam with an axially changing profile formed on the camshaft, an actuator that changes the position of the cam profile in the axial direction in response to engine operating conditions, a swinging rocker arm equipped with components that contact multiple valves, a sub-rocker arm supporting a roller follower that rotatably contacts the solid cam, and a sub-rocker support part that supports the swinging movement of the sub-rocker on the rocker arm (see for example, Japanese Published Patent Application H5-18221, pages 3-4 and FIG. 1).
Japanese Published Patent Application H10-18823 (see pages 3-4 and FIG. 1) discloses another type of variable valve mechanism that includes a solid cam camshaft that incorporates a variable low to high-speed profile that changes continuously along the axial direction, an actuator that changes the axial position of the camshaft in relation to engine operating conditions, and an arm that moves in synchronization with two or more adjacent valves and whose movement is dependent on the profile of the solid cam. The aforesaid arm incorporates a follower mechanism that follows positional changes in the linear contact angle of the rotating solid cam through a follower in contact therewith, and two or more contact members that press against the ends of two or more valves.
Japanese Published Application 2002-147241 (see pages 3-4 and FIG. 4) discloses another type of engine in which there is a positional relationship between a fuel injector and a cylinder head.
Currently known variable valve mechanisms of the type applied to internal combustion engines, such as those noted in Japanese Published Patent Application H5-18221 and Japanese Published Patent Application H10-18823, describe a mechanism that includes a camshaft onto which a three-dimensional cam (hereafter referred to as a 3D cam) is formed having a profile that varies along the axial direction, and valves that open and close according to the rotation of the 3D cam, wherein the amount of valve lift varies depending on the positional relationship between the 3D cam and valve stem. These variable valve mechanisms described by Japanese Published Patent Application H5-18221 and Japanese Published Patent Application H10-18823 employ a mechanism in which the valve is driven by the rotational movement of the 3D cam being transferred to the valve through a rocker arm.
Moreover, some internal combustion engines place the fuel injector as close to the combustion chamber as possible in an effort to lower exhaust gas emissions and improve combustion performance. For example, the fuel injector shown in Japanese Published Application 2002-147241 is located in the middle at the top of the cylinder in order to inject fuel directly into the combustion chamber.
These known variable valve mechanisms exhibit an undesirable characteristic in that the use of 3D cams to open and close valves through rocker arms has the effect of increasing the width (the transverse direction at a right angle to the axial centerline of the camshaft) of the cylinder head. Furthermore, increasing the width of the cylinder head makes it more difficult to locate the injector (which sprays fuel into the intake port leading to the combustion chamber) close to the combustion chamber.
In order to solve the shortcomings of the prior art, the present invention proposes a variable valve mechanism that axially supports the camshaft, on which a 3D cam is formed, at least on the intake port side of the cylinder head, locates the fuel injector in the part of the intake sidewall bordering the intake port of the cylinder head, and provides for a concave part, formed in the intake sidewall, that extends inward toward the intake camshaft at a location above the fuel injector. This structure prevents the sidewall from obstructing the installation of the fuel injector to the cylinder head, and allows the fuel injector to be located in closer proximity to the combustion chamber.